The present invention relates generally to the routing of information cross networks and, more particularly, to the determination of link state status in the routing of voice over frame-relay information across multiservice networks.
Until recently there has persisted a fundamental dichotomy between two main types of telecommunication networks. The first type of telecommunication network, the telephone network, switches and transports predominantly voice, facsimile, and modulation-demodulation system (modem) traffic. The public switched telephone network (PSTN) is an example of this type of network. Telephone networks are also deployed privately within organizations such as corporations, banks, campuses, and government offices. The second type of telecommunication network, the data network, switches or routes and transports data and video between computers. The Internet is an example of a public data network; data networks may be privately deployed.
Telephone networks were developed and deployed earlier, followed by data networks. Telephone network infrastructures are ubiquitous, however, and as a result data networks typically are built, to a limited extent, using some components of telephone networks. For example, the end user access link to a data network in some cases is implemented with a dial-up telephone line. The dial-up telephone line thus connects the end user computer equipment to the data network access gateway. Also, high speed digital trunks interconnecting remote switches and routers of a data network are often leased from telephone long-haul carriers.
Nonetheless, telephone and data network infrastructures are usually deployed together with limited sharing of resources, especially with regards to the core components of the networksxe2x80x94the switches and routers that steer the payloads throughout the networks. Furthermore, multiservice network switches are used to provide a data path, or interface, between multiple networks, each of which may operate using a different type of data or according to a different networking standard protocol. Examples of the networking protocols supported by these multiservice switches include, but are not limited to, frame relay, voice, circuit emulation, T1 channelized, E1 channelized, and Asynchronous Transfer Mode (ATM). The cost of this redundancy coupled with advances in data network technology has led, where possible, to integrated network traffic comprising voice, data, facsimile, and modem information over a unified data network. As such, a data network should now be able to accept, service, and deliver any type of data over its access links on a random, dynamic basis using a minimum set of hardware on a single platform. The problem remains, however, that a typical router or concentrator routes data through packet switch networks while voice and video traffic are routed through circuit switch networks, each of which uses different physical switch equipment.
The aforementioned desire to integrate network traffic and transport the traffic over a unified data network has heretofore resulted in a limited sharing of network resources, especially with regards to the core network switches and routers that steer the payloads throughout the networks. As such, a data network should now be able to accept, service, and deliver any type of data over its access links on a random, dynamic basis using a minimum set of hardware on a single platform. Typical routers include a group of the same dedicated hardware and software resources for each channel of information processed through the router. This scheme, however, limits the number of information channels that can be processed by a router. Furthermore, this scheme wastes router resources because, as the router accommodates many different types of data, and all of the different types of data do not require the same resources for processing, many allocated resources stand idle on the typical router.
Consequently, a router is desired that provides for dynamic allocation of router resources among the received channels of information on an as-needed basis, wherein the cost, size, and complexity of the router is reduced by minimizing the duplication of resources among router channels.
Conventional routers attempt to maximize the use of resources using the concept of virtual circuits. A virtual circuit includes hardware and software on the router that performs router functions for a particular incoming or outgoing call. Many virtual circuits may be multiplexed onto a single physical interface. This is a well-known Frame Relay concept as defined in Frame Relay Forum implementation agreement (FRF).1 and International Telecommunications Union (ITU) Q.922. Because voice data may be routed through many virtual circuits, it is important to have knowledge of link state information for each of the virtual circuits multiplexed onto a physical carrier. FRF.1 addresses this problem at the virtual circuit level by defining a Local Management Interface (LMI), which provides link state information for each of the virtual circuits multiplexed onto the physical interface carrier.
FRF.11 defines a mechanism for multiplexing up to 255 voice subchannels, or FRF.11 virtual channels, onto a single Frame Relay virtual circuit. The FRF.11 definition is similar in concept to the multiplexing of several FRF.1 virtual circuits onto a single physical interface that occurs in the FRF.1 definition. Just as FRF.1 virtual channels can be switched between physical interfaces, voice virtual channels may be switched between Frame Relay virtual circuits. In conventional networks, however, the link state of the carrier is not reflective of the link state of the channel connections. FRF.11 does not define a mechanism similar to LMI for determining the link state of voice channels. Accurate and dynamic link state knowledge of voice channels is critical to the successful routing of voice streams through an FRF.11 network, however, because routing decisions must be made at every switch point.
Channel link state cannot be determined solely on the basis of receipt of voice data or failure to receive voice data. Failure to receive voice data may simply be an indication that there was no voice data to send, rather than an indication of path failure. It is therefore desirable to determine a link state of backup or standby routes at the channel level. It is also desirable to determine a link state of these routes before voice information is sent over the routes and before failure occurs on primary routes.
It is therefore an object of the invention to integrate data, voice, and video onto public and private packet-based or cell-based multiservice data networks comprising Frame Relay, Asynchronous Transfer Mode (ATM), High-level Data Link Control (HDLC), Internet Protocol (IP), and Time Division Multiplexed (TDM) networks, and leased line carrier services.
It is a further object of the invention to provide a trunk that is software configurable at the physical and protocol levels to support T1/E1, Frame Relay, ATM, HDLC, IP, and TDM services.
It is a further object of the invention to provide a method and apparatus for dynamically determining multi-level link state for Frame Relay networks.
These and other objects of the invention are provided by a Multiservice Access Concentrator (MAC).
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description which follows below.
In one embodiment, the present invention includes a method for determining link state for permanent calls in an FRF.11 voice over data network at the virtual voice channel level. This is a capability not present in FRF.11, which includes a management mechanism for determining link state of virtual circuits, but does not include a mechanism for determining link state of virtual channels. One embodiment uses a standard FRF.11 signaling frame with a status indicator bit to signal that a channel is a primary operative channel or an alternate operative channel. The signaling frames are sent end to end through the network by an initiator device along a primary data path and all alternate data paths. If a primary or alternate path is operative, a reciprocator device returns the signaling frame along the operative path. The initiator determines by receipt or non-receipt of the signaling frames which paths are operative at any time. This allows the initiator to quickly detect primary path failure and switch to an operative alternate path.